Okay, so one of the gorgeous multicolored half moon I have. When I fist got him I put him in this 1 gal bowl. Everything was fine. He made bubble nest and was always circling the bow enthusiastically. Finally, I got him his own ten gallon tank, I was so sure he'd love all the space (seeing how happy he was with his little bowl) but he wasn't, at all. He started being a tail bitter and just hid under the little wolf figurine I gave him. "Maybe he was just hungry", I thought. I switched him to a bloodworm only diet, since he always has a hard time eating the pallets and doesn't like the frozen food. But still, the tail biting continued.

Later on I made a not so wise decision to add dividers to the tank. So his roommate was a non-aggressive hmpk dumbo. This he was not thrilled with. Two days later I saw he was biting way too much. Now he lives in a 1 & 1/2 gallon bowl with his wolf, bamboo, and marimo. He even has a little loop-DE-loop routine when he swims by the bamboo. His tail is almost back to normal, now.

I almost wonderif one of my bettas is like this. He hardly utilizes his 5 gallon space ans likes to sit in one spot. I am thinking of trying switching him into a 1.7 and putting that fish in the 5. Some fish are so weird!

Some fish just won't thrive in larger spaces, it's overwhelming to them. I have a CT that will panic in a 2.5 gal, and he'll hide in the corner, and won't come out to eat, so he stays in a 1 gal, because that's what he's comfortable with.

How much cover did the 10 gallon tank offer? I've found that most people who run into difficulties with transitioning bettas to bigger tanks, don't provide enough areas of cover for their fish.

Bare or sparsely decorated tanks can be unsettling for a lot of fish, not just bettas.

Some bettas really need to have a definable territory and plenty of cover to feel comfortable in a larger space. Also, because the 10 gallon requires the betta to spend more time swimming, males with larger finnage can sometimes start to self-mutilate and tail bite.

The presence of another male probably added to his stress and wouldn't have allowed him to feel comfortable.

However, as long as the bowl water is kept clean and heated, 1.5 gallons is an adequate space for a single male betta.